1. Field of the Invention
The present invention relates to a toner set used for full-color image-forming apparatuses, such as full-color copying machines and full-color printers, and especially for those full-color image-forming apparatuses in which toner images formed on an image-supporting member are pressed and transferred onto an intermediate transfer member in an overlapped manner for each color, and the toner image, transferred onto the intermediate transfer member, are pressed and transferred onto a recording member.
The present invention also concerns a full-color image-forming method in which the toner set is used.
2. Description of the Prior Art
Conventionally, image-forming apparatuses, such as copying machines, printers and facsimiles, have been widely used. In such image-forming apparatuses, an image-forming process is carried out by an electrophotographic system in which an electrostatic latent image formed on a photosensitive member is developed by toner and the toner image is transferred onto a recording member such as recording paper,, etc. Moreover, in recent years, full-color image-forming apparatuses, such as full-color copying machines and full-color printers, which reproduce full-color images by using toners having a plurality of colors, have been widely used.
Referring to a full-color image-forming apparatus shown in FIG. 2, a brief explanation will be given of these apparatuses. Upon formation of a full-color image, when a printing operation is started, a photoconductive drum 10 and an intermediate transfer belt 40 are rotationally driven with the same peripheral velocity and the photoconductive drum 10 is charged to a predetermined electric potential by a charging brush 11.
Successively, exposure for a yellow image is carried out by a laser scanning optical system so that an electrostatic latent image of the yellow image is formed on the photoconductive drum 10. This electrostatic latent image is immediately developed in a developing device 31Y, and the toner image is pressed and transferred onto the intermediate transfer belt 40 at a primary transfer section. Immediately after the primary transferring process has been finished, switching is made to a developing device 31M in the developing section D, and then exposure, developing and a primary transferring process for a magenta image are carried out. Moreover, switching is made to a developing device 31C, and exposure, developing and a primary transferring process for a cyan image are carried out. Furthermore, switching is made to a developing device 31Bk, and exposure, developing and a primary transferring process for a black image is carried out. In each of the primary transferring processes, the toner image is superimposed on the intermediate transfer belt 40.
After the final primary transferring process has been completed, a recording sheet S is sent to a secondary transfer section, and a full-color toner image, which has been formed on the intermediate transfer belt 40, is pressed and transferred onto the recording sheet S. After completion of the secondary transferring process, the recording sheet S is transferred to a belt-type contact-heating fixing device 70 in which the full-color toner image is fixed on the recording sheet S, and then is discharged onto the upper surface of a printer main body 1.
With respect to full-color developing toners, toners including a yellow toner, a magenta toner, a cyan toner and a black toner are loaded into respective developing devices for the respective colors. With respect to the shape of toner particles contained in the respective toners, all the toners have a uniform shape.
However, when the above-mentioned full-color developing toners and the full-color image-forming apparatuses are used, the transferring properties tend to deteriorate due to fluctuations in environmental conditions, such as temperatures and moisture, and transferring conditions at the time of the primary and secondary transferring processes, causing image losses in superimposed toner images having two or more colors and scattering of toner; this causes image noise such as defective images and image-fogging in the resulting full-color copied images. Moreover, another problem is raised in that in the case of a spherical particle shape of respective color toners, residual toner on the photosensitive member from the primary transferring process deposits in the gap between the surface of the photosensitive member and a cleaning member, causing a defective cleaning process (insufficient sweeping).
In order to solve the above-mentioned problems, attempts have been made to regulate setting conditions on the transferring process, cleaning, etc.; however, they have failed to solve all the above-mentioned problems at the same time, and restrictions imposed by the various conditions tend to raise new problems.
An objective of the present invention is to provide a toner set with superior transferring properties and cleaning properties, which does not cause image losses in toner images and toner scattering in the primary and secondary transferring processes, and can eliminate image-fogging in full-color copied images.
Another objective of the present invention is to provide a full-color image-forming method having superior transferring properties and cleaning properties, which does not cause image losses in toner images and toner scattering in the primary and secondary transferring processes, and can eliminate image-fogging in full-color copied images.
The present invention relates to a toner-set comprising yellow toner, magenta toner, cyan toner and black toner, in which
the black toner comprises black toner particles comprising at least a binder resin and a black colorant and having a standard deviation of degree of roundness of not more than 0.045;
the yellow toner comprises yellow toner particles comprising at least a binder resin and a yellow colorant and having a standard deviation of degree of roundness of not more than 0.045 and an average degree of roundness larger than that of the black toner particles,
the magenta toner comprises magenta toner particles comprising at least a binder resin and a magenta colorant and having a standard deviation of degree of roundness of not more than 0.045 and an average degree of roundness larger than that of the black toner particles, and
the cyan toner comprises cyan toner particles comprising at least a binder resin and a cyan colorant and having a standard deviation of degree of roundness of not more than 0.045 and an average degree of roundness larger than that of the black toner particles.
The present invention also relates to a method for forming full-color images suitable for use of the toner-set.